The present invention generally relates to an apparatus and method for detection of radiation.
The invention is usable in a variety of fields including e.g. medical radiology, computerized tomography (CT), microscopy, and non-destructive testing.
Gaseous detectors, in general, are very attractive at photon energies lower than approximately 10 keV. The main advantages of gaseous detectors are that they are cheap to manufacture compared to solid state detectors, and that they can employ gas multiplication to strongly (on orders of magnitude) amplify the signal amplitudes. However, at energies exceeding 10 keV the gaseous detectors are less attractive as the stopping power of the gas decreases rapidly with increased photon energy. This results in a heavily deteriorated spatial resolution due to parallax errors of the conversion points of the often divergent incident beam of radiation, and due to extended tracks of so-called long-range electrons, which are created as a result of the X-ray absorption.
An improved spatial resolution is achieved by a gaseous detector for use in planar beam radiography, in which electrons released by interactions between photons and gas atoms can be extracted in a direction essentially perpendicular to the incident radiation. A detector of such a kind is described in our copending international application WO99/23859 entitled A method and a device for planar beam radiography and a radiation detector and filed on Oct. 19, 1998.
Such detector comprising interactions between photons and gas atoms need, however, to be relatively deep and comprise a pressurized gas. Further, such detector need to use a gas optimized both for interaction with the incident radiation and with accelerating electrons (during the electron multiplication).
An object of the present invention is to provide an apparatus and method for detection of ionizing radiation, which employ avalanche amplification, and by which measurements of high spatial resolution are obtainable.
A further object of the present invention is to provide an apparatus and method for detection of ionizing radiation, which exhibit high signal-to-noise ratios.
Still a further object of the invention is to provide an apparatus and method for detection of ionizing radiation, which are sensitive and can thus be used employing very low X-ray fluxes.
Yet a further object of the present invention is to provide an apparatus and method for detection of ionizing radiation, which are effective, fast, accurate, reliable, easy to use, and of low cost.
Still a further object of the invention is to provide an apparatus and method for detection of ionizing radiation, in which electrons released during detection, can be extracted in a direction essentially perpendicular to the incident radiation. Hereby it is possible to obtain a particularly high spatial resolution.
Yet a further object of the invention is to provide an apparatus and method for detection of ionizing radiation, which can operate at high X-ray fluxes without performance degradation and has a long lifetime.
These objects among others are, according to the present invention, attained by apparatus and methods as claimed in the appended Claims.
By employing avalanche amplification of electrons released from a photocathode of the detection apparatus a particularly sensitive apparatus and method are achieved, which provide for the employment of extremely low doses of radiation, still obtaining signal levels high enough for construction of images, which exhibit very low noise levels.
A further advantage of the invention is that the inventive detector apparatus is not very sensitive to magnetic fields.
Yet a further advantage of the invention is that it provides for the manufacture and use of sensitive large-area detector apparatus to a low cost.